Burn pit is probably the easier option in most scenarios. In most cases it’s a lot easier to dig a hole deep enough to bury the ashes of a bunch of cows than to have to prep the bodies of all the cows, bury them under 6 ft of soil, and then sanitize the soil around it.

I imagine the only time you wouldn’t go with the burn pit is if it’s too windy, or in a location where you’d be worried about starting a wild fire on top of a biohazard.